I was reading the RFE about having molochs crush trees when moving onto spaces with regular trees on them, specifically where someone noted that trees only really appear in towns and the wilderness, and I had a bit of inspiration.

One of the big problems with the "Bridge-building" skill is the need to carry very heavy logs all the way from the wilderness to the location with the river to be crossed. This is a very slow process, and often problematic.

My suggestion is this - add trees to levels that have rivers (including the water temple level). It makes some sense in terms of the world - with the magical light suffusing the dungeons, the only thing a tree really still needs to survive is a healthy amount of water. If there's a river on that level, that will provide more than enough for the trees to thrive.

It also makes bridge building a much more useful skill, without needing to dramatically alter how it works (a bit of tweaking would still be appreciated).

Other thoughts in connection with this:

1. Once deep enough (DL above some value), there could be a small chance of a tree being generated as an animated tree.
2. Any level with regular water spaces as well as regular land spaces should have some chance of having a tree put into each regular land space. Note that this doesn't include the Tomb of the High Kings, as the water there is not regular water. It also does not include the Water Dragon's Lair, as there is no regular land space in there.
3. In addition to being a source of wood, perhaps DV could be a little higher for any creature (including the PC) standing on a Tree space - the reasoning being that the creature/PC is able to use the tree as an additional form of defense, ducking around the trunk and using it as a kind of shield. The effect needn't be strong, but it would add a little extra flavour, again, to trees.